Do I need to spray foam the ceiling of my crawl space to help winterize it?

Whether or not you need to insulate the ceiling of a crawlspace depends on the temperature you plan to keep it at. If it will be warm like the house above then there is no reason to insulate between the two spaces, you could just treat it all as interior conditioned space. That way you don’t need to worry about draining pipes to avoid freezing for any winters you keep it warm. And a good starting place for all crawlspace improvements is here –

Crawl Space Insulation Tips for Insulating Crawlspaces Properly

One option would be to insulate the walls and concrete slab floor with spray foam, that would act as a vapour barrier as well as air barrier and thermal barrier. It hardens enough that you can walk on it if necessary, and it sounds like a space you won’t even be able to walk on or need to access very often.

Spray foam used to be about the most harmful insulation material but there has been some big changes in the industry to reduce the green house gas emissions of spray foam, so if you go that route I would pitch you the idea of choosing a spray foam with blowing agents that reduce greenhouse gas emissions.

And the last point I would bring up, would be the potential risk that comes with insulating old block foundations that never had any insulation in the past. Where are you building (as in what is your climate zone) and what is the condition of the wall? Are there cracks in the joints? Block foundation walls are not as strong as poured concrete, so if suddenly they are exposed to the seasonal freeze / thaw cycle then there is a risk of cracking in the joints. I’m not trying to talk you out of it, just have a look first at the general condition and if its damaged then I’d have a pro look at it first before going ahead with work. Best is always to insulate the outside of foundations so you keep the wall warm but we realize that isn’t always a viable option. Just putting it out there.

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